Internal combustion engines are supplied with a mixture of air and fuel for combustion within the engine that generates mechanical power. To maximize the power generated by this combustion process, the engine is often equipped with a turbocharged air induction system. A turbocharged air induction system includes a turbocharger that uses exhaust from the engine to compress air flowing into the engine, thereby forcing more air into a combustion chamber of the engine than the engine could otherwise draw into the combustion chamber. This increased supply of air allows for increased fueling, resulting in an increased engine power output.
A turbocharger generally comprises a compressor wheel mounted on one end of a single shaft in a compressor housing and a turbine wheel mounted on the other end of the shaft in a turbine housing. Typically, the turbine housing is formed separately from the compressor housing. A bearing housing is connected between the turbine and compressor housings for containing bearings for the shaft. The turbine housing receives exhaust gas from the engine and directs it to the turbine wheel which is driven by the exhaust gas. The turbine assembly thus extracts power from the exhaust gas and drives the compressor.
The turbine housing may also include a nozzle ring that surrounds the turbine wheel and is operable to adjust the flow rate of the exhaust gas before it reaches the turbine wheel. Turbochargers typically use a nozzle ring that is a separate investment cast component made from stainless steel. However, such castings can be relatively expensive, adding significant cost to the turbocharger. Investment cast nozzle rings made from stainless steel also can be a thermal mismatch with adjacent components which can create problems as the components expand and contract as a result of exposure the hot engine exhaust gases. Moreover, expensive investment cast nozzle rings have nozzle throat areas with set sizes which can limits the flexibility of the turbocharger with regard to matching the performance of the engine.